Unlike the more powerful nuclear reactors capable of distributing an electrical power in excess of 1000 MW, the small and medium modular reactor sector, commonly referred to as SMRs which stand for Small Modular Reactors, is undergoing substantial expansion. Many designs of SMR are in progress, generally in the 50 to 700 MW range (<300 MW for small reactors; <700 MW for medium reactors). Being less expensive and more flexible than traditional installations, SMRs provide the answer to the increasing need for electrical energy, particularly in the developing countries.
The modular construction of the SMRs allows production capacity to be increased incrementally by using the number of modules that suits the need. Being more compact, they can be partially prefabricated prior to transport and assembled on the final end-user site. Designed as a plug and play solution, SMR installations can be built more quickly, offering greater flexibility in terms of financing, in terms of the scope of installation work to be carried out on site, in terms of the size and the end-use.
There are a number of reactor types envisioned for SMRs particularly pressurized water reactors (PWRs), high temperature reactors (HTRs) or even molten salt reactors (MSRs). In PWRs, the ordinary water that constitutes the coolant is kept liquid under high pressure, of the order of 150 bar. In the primary circuit, the water collects the heat produced by the nuclear fuel and transmits it to the fluid of the secondary circuit using steam generators. In the integrated PWRs envisioned for the SMRs, one or more steam generator(s) is/are situated in the same enclosures as the reactor. The heat from the reactor is transmitted by the secondary circuit to a steam turbine which drives an alternator tasked with producing electricity.
One or more primary pumps circulate the water through the primary circuit, between the reactor core and the steam generators. The primary coolant pump is a component essential to the operation and safety of a PWR facility. The design of SMRs entails a rethink of the architecture of the primary pump because the architecture of an integrated PWR which has the reactor, the primary circuit and the steam generators in one module imposes new requirements, both geometric and functional, and in terms of durability, or safety requirements.
The ambitious specification sheet for a reactor that is simple, compact, inexpensive and meets the most stringent safety requirements, is logically passed on to its constituent parts. Existing primary pumps are illustrated to this new requirement. By way of nonlimiting example of the present invention, a motor-driven primary pump suited to an SMR has, by way of functional requirements, a durability of 60 years, a motor-driven pump inlet fluid temperature of between 300 and 350° C., an operating pressure of 140 to 160 bar, a coolant density of between 600 and 700 kg/m3, and a raft of geometric requirements (e.g. the ability to mount vertically or horizontally, the overall size envelope), installation requirements (e.g. the fact that it must not be installed by welding, that it must be possible to disconnect it completely from outside the reactor, without components remaining inside the enclosure), and external requirements (e.g. seismic requirements).
Thus, it is desirable to have a motor-driven primary pump that meets these new and ambitious requirements. The suitable motor-driven primary pump will need to be of simple design, robust, economical, compatible with mass production, and meet the most stringent functional and regulatory requirements.